Quantitative dynamics of Salmonella and E. coli in feces of feedlot cattle treated with ceftiofur and chlortetracycline

PLoS One. 2019 Dec 2;14(12):e0225697. doi: 10.1371/journal.pone.0225697. eCollection 2019.

Abstract

Antibiotic use in beef cattle is a risk factor for the expansion of antimicrobial-resistant Salmonella populations. However, actual changes in the quantity of Salmonella in cattle feces following antibiotic use have not been investigated. Previously, we observed an overall reduction in Salmonella prevalence in cattle feces associated with both ceftiofur crystalline-free acid (CCFA) and chlortetracycline (CTC) use; however, during the same time frame the prevalence of multidrug-resistant Salmonella increased. The purpose of this analysis was to quantify the dynamics of Salmonella using colony counting (via a spiral-plating method) and hydrolysis probe-based qPCR (TaqMan® qPCR). Additionally, we quantified antibiotic-resistant Salmonella by plating to agar containing antibiotics at Clinical & Laboratory Standards Institute breakpoint concentrations. Cattle were randomly assigned to 4 treatment groups across 16 pens in 2 replicates consisting of 88 cattle each. Fecal samples from Days 0, 4, 8, 14, 20, and 26 were subjected to quantification assays. Duplicate qPCR assays targeting the Salmonella invA gene were performed on total community DNA for 1,040 samples. Diluted fecal samples were spiral plated on plain Brilliant Green Agar (BGA) and BGA with ceftriaxone (4 μg/ml) or tetracycline (16 μg/ml). For comparison purposes, indicator non-type-specific (NTS) E. coli were also quantified by direct spiral plating. Quantity of NTS E. coli and Salmonella significantly decreased immediately following CCFA treatment. CTC treatment further decreased the quantity of Salmonella but not NTS E. coli. Effects of antibiotics on the imputed log10 quantity of Salmonella were analyzed via a multi-level mixed linear regression model. The invA gene copies decreased with CCFA treatment by approximately 2 log10 gene copies/g feces and remained low following additional CTC treatment. The quantities of tetracycline or ceftriaxone-resistant Salmonella were approximately 4 log10 CFU/g feces; however, most of the samples were under the quantification limit. The results of this study demonstrate that antibiotic use decreases the overall quantity of Salmonella in cattle feces in the short term; however, the overall quantities of antimicrobial-resistant NTS E. coli and Salmonella tend to remain at a constant level throughout.

Publication types

  • Randomized Controlled Trial, Veterinary
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Anti-Bacterial Agents* / administration & dosage
  • Anti-Bacterial Agents* / adverse effects
  • Bacterial Proteins / genetics
  • Cattle
  • Cephalosporins / administration & dosage
  • Cephalosporins / adverse effects
  • Chlortetracycline / administration & dosage
  • Chlortetracycline / adverse effects
  • Colony Count, Microbial
  • DNA, Bacterial / isolation & purification
  • Drug Resistance, Multiple, Bacterial
  • Escherichia coli Infections* / drug therapy
  • Escherichia coli Infections* / epidemiology
  • Escherichia coli Infections* / microbiology
  • Escherichia coli Infections* / veterinary
  • Escherichia coli* / drug effects
  • Escherichia coli* / isolation & purification
  • Feces / microbiology
  • Foodborne Diseases / prevention & control
  • Longitudinal Studies
  • Male
  • Microbial Sensitivity Tests
  • Prevalence
  • Red Meat / microbiology
  • Salmonella Infections, Animal* / drug therapy
  • Salmonella Infections, Animal* / epidemiology
  • Salmonella Infections, Animal* / microbiology
  • Salmonella* / drug effects
  • Salmonella* / genetics
  • Salmonella* / isolation & purification

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • ceftiofur
  • Cephalosporins
  • Chlortetracycline
  • DNA, Bacterial
  • invA protein, Bacteria

Grants and funding

Funded by BN; The field trial was funded by United States Department of Agriculture-National Institute of Food and Agriculture (NIFA)-Agriculture and Food Research Initiative (AFRI) (formerly Cooperative State Research, Education, and Extension Service (CSREES); grant numbers 2008-35201-30235 and 2008-35201-04682) entitled: “Novel pre-harvest interventions to protect antimicrobials of critical importance in human and veterinary medicine”. https://portal.nifa.usda.gov/web/crisprojectpages/0227723-novel-pre-harvest-interventions-to-protect-antimicrobials-of-critical-importance-in-human-and-veterinary-medicine.html; https://portal.nifa.usda.gov/web/crisprojectpages/0214812-novel-pre-harvest-interventions-to-protect-antimicrobials-of-critical-importance-in-human-and-veterinary-medicine.html. HMS; The subsequent phenotypic and genotypic analysis of E. coli isolates was funded by United States Department of Agriculture-National Institute of Food and Agriculture-National Integrated Food Safety Initiative (NIFSI); grant number 2010-51110-21083) entitled: “Practical interventions to effectively manage antibiotic resistance in beef and dairy cattle systems: a fully integrated approach”. https://nifa.usda.gov/program/national-integrated-food-safety-initiative. SL, KN, HMS: The open access publishing fees for this article have been covered by the Texas A&M University Open Access to Knowledge Fund (OAKFund), supported by the University Libraries and the Office of the Vice President for Research. https://library.tamu.edu/services/scholarly_communication/Open_Access/oakfund.html. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.